This invention relates to telescoping work platforms. In particular, it relates to locking mechanisms for telescoping work platforms that are extended and retracted by hoist cables.
The conventional telescoping work platforms generally include three frames (stages): a base frame, a middle frame and a platform frame. The frames are operatively interconnected such that the middle frame can be raised above the stationary base frame and the platform frame can be raised above the middle frame. The raising and lowering of frames to their fully nested postions is accomplished by reeling a hoist cable onto a drum by means such as a crank. The hoist cable, anchored to the lower end of the platform frame, extends through a pulley mounted at the upper end of the middle frame and through a pulley near the top of the base frame to the drum.
When the work platform is in a fully nested position, the reeling of the hoist cable onto the drum causes the platform frame to lift. The platform frame is lifted until it comes in contact with stops which prevent further upward movement. The subsequent reeling of the hoist cable then causes the lifting of the middle frame until it reaches its fully extended position defined by appropriate stops.
To retract the platform from its fully extended position, the crank is rotated to release the hoist cable from the drum. As the cable is released, the middle frame is lowered, while the platform frame remains in a fixed position with respect to the middle frame. Once the middle frame reaches its fully nested position, a further release of the cable causes the lowering of the platform frame until it reaches its fully nested position.
When the work platform is in a fully or even partially extended position, the platform frame is at a relatively high elevation. Accordingly, it is essential to the safety of those using the work platform that the frames of the platform do not accidentally slip or fall from their fully extended positions.
A platform may be equipped with safety chains, the links of which are engaged by locking means in the event the hoist cable breaks. The safety chains prevent the platform from falling in the event of the broken cable. However, another problem may result when the owner or user of the platform neglects to properly maintain the platform. Specifically, a failure to maintain the platform can cause a build-up of rust and dirt along the guide tracks on which the frames are raised and lowered. Such build-up can cause premature raising or lowering of the middle frame. The premature raising or lowering of the middle frame creates an unstable condition where the weight of the user can cause an extended or partly extended sliding frame to fall to its fully nested position.
Accordingly, it is essential that the stages be lowered and raised in proper sequence. If the owner or user of the platform follows the instructions in the operator instruction and maintenance manual the proper sequence is assured. Many owners or users, however, ignore and elect not to follow instructions and allow the guide tracks to rust and to accumulate a build-up of particles. The neglect can hinder the proper sequencing of staging.
The present invention provides a device for telescoping work platforms that alleviates problems and conditions caused by owner's or user's failures to maintain the work platform.
One object of the present invention is to provide a device which compensates for owner's or user's failures to properly maintain the work platform and prevents improper sequencing of the platform which is not properly maintained.
A further object of the present invention is to provide a device for the work platform which is reliable and which requires minimal maintenance.
Still another object of the present invention is to eliminate unstable conditions in raising or lowering work platforms even if they are not properly maintained.
Still another object of the present invention is to provide an automatic device which need not be specially activated by the user and which does not inconvenience the user.
Other objects of the present invention become apparent to those skilled in the art upon studying this disclosure.